As a reminder, all house committees, except for the Judiciary Committee, may issue subpoenas only in regards to either existing or pending legislation. The Judiciary Committee may issue subpoenas for any matter whether it is involved with legislation or not. As the story points out, now all the other witnesses now have a road map of how not to be forced to testify.

https://www.breitbart.com/politics/2019/11/08/dems-pull-subpoena-for-ex-trump-adviser-who-took-it-to-court-lawsuit-would-delay-impeachment/